Highly efficient wireless energy harvesting system using metamaterial based compact CP antenna

This paper presents a highly efficient 2.4 GHz wireless energy harvesting system comprising of a metamaterial based circularly polarized (CP) antenna and a power management circuit. The antenna is designed at 2.4 GHz using a circular slotted truncated corner square patch radiator placed on reactive impedance surface (RIS) for antenna size miniaturization, better impedance matching and to improve the front-to-back ratio. The power management system integrates a matching circuit with a single stage Dickson charge pump and an ultra low power with high efficiency DC/DC boost converter/charger. The Dickson charge pump uses three Schottky diodes to minimize the losses at high frequency. The DC-DC converter (BQ25504) is capable of acquiring and managing low power levels. The measured axial ratio (boresight) is below 3-dB for the entire 2.40-2.48 GHz band and the 10-dB return loss band is from 2.35-2.49 GHz. The gain (boresight) of the antenna is around 4.6 dBic at 2.44 GHz. The proposed antenna shows an improvement in front-to-back ratio of around 3 dB with size reduction of approximately 22%. The power management system generates an output voltage level of 1.5 volts at -10 dBm and 4 volts at 0 dBm input RF power respectively. The overall efficiency of the proposed energy harvesting system is above 28%.